Gene transfer to the airways of patients with cystic fibrosis (CF) could represent a major therapeutic advance for this lethal disease. Although previous work in vitro, in animals and in people with CF has established the feasibility of gene transfer, it has also revealed the limitations of current approaches. The two greatest barriers are limited efficiency of gene transfer from the apical surface of differentiated airway epithelia and limited persistence of expression. The projects in this program utilize novel approaches and models to overcome these barriers. Recent work showed that adeno-associated viruses-5 (AAV5) vectors target the apical surface of differentiated airway epithelia, which makes them an attractive vector. Project by Welsh (subproject 0001) focuses on overcoming the limited packaging capacity of AAV vectors and will test the long-term potential of AAV5 vectors to correct the CF C1- transport defect. In Project by Zabner (subproject 0004), the investigators will study how AAV5 interacts with its apical membrane receptors, sialic acid and PDGF-receptor. They combine this with a structural analysis of the virus and its receptor. Project by McCray (subproject 0005) takes a related approach to achieving apical targeting and long-lasting expression by developing LCMV-pseudotyped lentivirus vectors. They investigate the virus:receptor interactions and will test the ability to achieve persistent expression in airway epithelia. Our ability to answer several crucial questions about gene transfer has been hampered by the lack of an animal model that faithfully reproduces the lung disease found in humans with CF. Project by Welsh (subproject 0006) addresses this problem by developing a porcine model of CF. The PPG benefits from outstanding support by the In Vitro Models and Cell Culture Core, the Gene Transfer Vector Core, and the Administrative Core. These studies will take us closer to our long-term goal of developing new therapies for people who suffer from CF.